In longwall mining, a plurality of conveyor pans are connected in an end-to-end, modular relationship for handling the mined minerals, such as coal. In addition to receiving the mineral as it is won for conveying away from the face, the mating pans also serve as a guide track for the haulage apparatus of the mining machine or shearer as it reciprocates back and forth.
To provide an efficient and effective conveyor system, the mating pans must interconnect in such a way as to withstand the substantial forces present during a typical mining operation, such as those created by the above-described motion of the mining machine. More specifically, the connection must resist tensile forces to prevent the pans from separating, while permitting a limited amount of up-and-down or toggling movement between mating pans to accommodate different mining conditions encountered, such as inevitable variations in the mine floor.
It is common in the art to use a releasable coupler placed between mating pans to provide this function. One of the most common couplers has an elongated shank and opposed enlarged ends, thus forming a dog bone shape. The coupler is retained in similarly shaped first and second recesses which cooperate between the mating pans. This arrangement allows the desirable up-and-down movement, while resisting the large tensile forces tending to cause pan separation.
In addition to the above-described tensile force, the mating pans are also subjected to significant vibrations during the mining operation. If not properly secured in place, jarring of the coupler caused by these vibrations can cause forceful ejection from the recesses. Of course, this allows the mating pans to separate and results in a conveyor system failure.
Thus, as should be appreciated from the above discussion, there is a recognized need to securely hold the dog bone type coupler in the recesses to prevent the deleterious downtime of the conveyor system. However, a competing need is ease of installation and removal. This is important for efficiently setting up or taking down the conveyor system, or adding or subtracting individual pans, as may be required during a particular mining operation.
Previously, others have proposed a number of solutions in an attempt to simultaneously meet both of these needs. Typical designs include pivoting one end of the coupler into a cavity formed in the first recess, thus providing a fixed first end. The second end swings free into the second recess, and a separate, removable I-plate is used to retain and lock it in place. In some prior art arrangements, these I-plates are wedge shaped to try to help hold the coupler in place. Because these plates still tend to fall out due to vibration, some designs also include a tethered R-clip or pin that is used to extend through mating apertures in the pan and the plate for locking. In later designs, the plates are permanently pivoted on a pin transverse to the longitudinal axis of the coupler and may or may not be securely locked in place. Examples of such proposals are found in U.S. Pat. No. 5,658,085 to Merten et al., issued Aug. 19, 1997, U.S. Pat. No. 5,287,955 to Steinkuhl et al., issued Feb. 22, 1994, and U.S. Pat. No. 4,733,771 to Grundken et al., issued Mar. 29, 1988.
While these designs offer some improvement in securing the coupler in the recesses, limitations remain. First of all, ease of coupler installation/removal is generally lacking. For instance, the need for a plate to be pivotally mounted on a pin leads to the disadvantage that the I-plates tend to jam due to debris and coal fines collecting in the exposed end of the recess. The operators, especially under time limitations to meet quotas, tend to try to force the plate into position bending or skewing the mounting pin and/or plate. In addition, a separate locking pin on the plate that is required to hold the plate in place complicates the process even more since it is typically very small and hard to manipulate. Another disadvantage is that in some instances, a special tool is even required to manipulate the pin to lock or unlock the plate. Moreover, even with a tool, it must be realized that conditions on the mine floor simply do not permit a worker to easily and efficiently complete such a pinned connection. Thus, pan installation/removal time and maintenance costs are substantially increased when these prior art arrangements have to be used.
Furthermore, in each of these designs, since the retaining I-plate is permanently attached, it is not easily replaceable when it becomes damaged. In addition to possible abuse by the operators in trying to overcome a jammed plate, repeated tension loading, vibration, and locking/unlocking creates deleterious wear on the plate and/or the two pins, thereby substantially reducing the locking integrity of the conveyor system. As the debris and fines of the minerals work into the cervices, not only is jamming a problem, but the abrasive effect serves to accelerate the wearing of these parts, especially the pivot connection. Eventually it is necessary to make radical repairs, such as drilling and replacement of the I-plate/mounting/locking pin assembly. Also, these prior art I-plate assemblies, in order to properly perform the retaining function, must be reworked to close tolerances since the feature of being permanently attached to the pan does not provide any leeway when they are being locked or unlocked against the coupler. Of course, these shortcomings further increase maintenance costs and may lead to significant production downtime.
Thus, a need is identified for an improved, simplified coupling assembly that interconnects conveyor pans placed in an end-to-end relationship for use in a longwall mining conveyor system. The coupling assembly would securely hold the pans together such that tensile forces are resisted, while permitting a limited amount of up-and-down movement between mating pans to accommodate varying mine conditions. In addition, installation of the coupling assembly would be simple, thereby easy assembly/disassembly is accomplished, allowing pans to be easily and efficiently added to or taken away from the system. Further, the assembly would be long-lasting and would utilize a minimum number of components that are easy to manipulate, can be adjusted and are relatively inexpensive to fabricate.